Electromechanical rear derailleur

ABSTRACT

An electromechanical rear derailleur is provided for a bicycle, including a base member for attachment to the bicycle along a mounting axis. A movable member has a cage assembly attached thereto. A linkage is provided including pivot axes oriented substantially perpendicular to the mounting axis, the linkage coupling the movable member to the base member and operative to enable movement of the movable member relative to the base member in a direction substantially parallel to the mounting axis. A power source powers an electric motor connected thereto and a transmission is coupled to and actuated by the motor to move the movable member.

BACKGROUND OF THE INVENTION

This invention relates to bicycles and bicycle derailleurs. Inparticular the invention relates to electromechanical rear derailleursfor bicycles.

SUMMARY OF THE INVENTION

The invention provides, in one aspect, an electromechanical rearderailleur for a bicycle, including a base member attachable to thebicycle along a mounting axis. A movable member includes a cage assemblyattached thereto. A linkage includes pivot axes oriented substantiallyperpendicular to the mounting axis. The linkage coupling the movablemember to the base member is operative to enable movement of the movablemember relative to the base member in a direction substantially parallelto the mounting axis. A power source is provided with a motorelectrically connected to the power source, and a transmission iscoupled to and actuated by the motor to move the movable member.

Other aspects of the invention provide a rear derailleur wherein thepower source is disposed on or in the base member. The linkage mayinclude an outer link member and an inner link member. The linkage mayinclude link pins on which the linkage pivots, the link pins definingthe pivot axes. The transmission may include a plurality of gearsrotatable about a plurality of gear axes, respectively, wherein the gearaxes are substantially parallel to the pivot axes. The transmission maybe disposed on or in the base member. The motor may be disposed on or inthe base member. The power source may be disposed on or in the basemember. The linkage may include an outer link member and an inner linkmember. The rear derailleur may further include a clutch between themovable member and the transmission, the clutch moving the movablemember responsive to operation of the transmission. The clutch mayinclude a drive arm coupled to the transmission and a clutch spring incontact with the drive arm. The transmission may include an output gearand the drive arm is coupled to the output gear. The clutch spring maybe disposed on the inner link member. The clutch spring may be disposedabout the link pin that attaches the inner link member to the movablemember. The motor may have a motor shaft with a motor shaft axis that isperpendicular to the pivot axes. The linkage may include link pins onwhich the linkage pivots, the link pins defining the pivot axes, whereinthe pivot axes are substantially parallel to the mounting axis and thetransmission includes a plurality of gears rotatable about a pluralityof gear axles, respectively, wherein at least some of the gear axleshave gear axle axes that are substantially parallel to the pivot axes.

The invention also provides in an alternative embodiment anelectromechanical rear derailleur for a bicycle, including a base memberattachable to the bicycle. A movable member is provided having a cageassembly attached thereto. A linkage is provided coupling the movablemember to the base member and operative to enable movement of themovable member relative to the base member. The derailleur includes apower source and a motor electrically connected to the power source. Atransmission is coupled to and actuated by operation of the motor tomove the movable member and a position detector is provided, including amagnet rotated by the transmission, a sensor to sense rotation of themagnet, a magnet guide sized and shaped to guidingly receive a portionof the magnet and position the magnet within an effective range of thesensor.

Alternatives include wherein the rear derailleur includes a magnetholder disposed in the rear derailleur, the magnet held by the magnetholder. The magnet holder may be coupled to the transmission. The rearderailleur may further include a PC board positioned in the base memberand wherein the sensor is disposed on the PC board in position to sensemotion of the magnet. A magnet guide may be disposed on the PC board andthe magnet extends from the magnet holder. The magnet holder may beattached to a position detector gear. The position detector gear may bein contact with and actuated by an output gear of the transmission. Therear derailleur may further include a position detector gear biasinggear disposed in the derailleur and coupled to the position detectorgear to reduce backlash thereof.

These and other features and advantages of the present invention will bemore fully understood from the following description of one or moreembodiments of the invention, taken together with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a rear derailleur according to the invention installed on abicycle.

FIG. 1a is the rear derailleur shown partially-actuated.

FIGS. 2a, b are two top views of a linkage of the derailleur at theoutboard and inboard extremes of its travel, respectively.

FIG. 3 is a section view of two linkage pivot pins located at the “B”knuckle of the derailleur through section E-E of FIG. 2 a.

FIG. 4 is a section view of the two linkage pivot pins located at the“P” knuckle through section F-F of FIG. 2 a.

FIGS. 5a, b are perspective views of the derailleur with the powersource installed (5 a) and removed (5 b), respectively. The cage is notshown for clarity.

FIGS. 6 a, b, c are mechanical and electrical connections between thepower source and the derailleur, and also show the sequential procedurefor removing the battery from the derailleur through section D-D of FIG.2 a.

FIG. 7 is an exploded view of a gearbox assembly of the derailleur.

FIG. 7a is a top view of the gearbox assembly.

FIG. 8 is a perspective view of a motor module of the derailleur.

FIG. 8a is a top view of the motor module.

FIG. 8b is a side view of the motor module.

FIG. 9 is a section view of the motor module along section H-H of FIG.8b showing the motor/worm/worm-gear arrangement.

FIG. 10 is a section view of the gearbox assembly through section K-K ofFIG. 7a showing three (3) of the gears/axles.

FIG. 11 is a section view of the gearbox assembly through section J-J ofFIG. 7a showing the parts relating to the position detector/magnet.

FIG. 12 is a section view of the motor module through section G-G ofFIG. 8a showing an element for locating the position detector chiprelative to the position detector magnet.

FIG. 13 is a section view of the gearbox assembly through section A-A ofFIG. 1a showing a button and its actuator assembly and, in addition, aLED and lens.

FIG. 14 is a section view of the derailleur assembly through section B-Bof FIG. 1a showing the low limit screw.

FIG. 15a is a section view of the derailleur assembly through sectionC-C of FIG. 1a showing the clutch in the non-actuated position.

FIG. 15b is a section view of the derailleur assembly through sectionC-C of FIG. 1a showing the clutch in a partially actuated position.

FIG. 15c is a section view of the derailleur assembly through sectionC-C of FIG. 1a showing the clutch in its fully actuated position, withfurther movement prevented by a hard stop between the drive arm and theinner link.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will herein be described with reference tothe drawings. It will be understood that the drawings and descriptionsset out herein are provided for illustration only and do not limit theinvention as defined by the claims appended hereto and any and all theirequivalents. For example, the terms “first” and “second,” “front” and“rear,” or “left” and “right” are used for the sake of clarity and notas terms of limitation. Moreover, the terms refer to bicycle mechanismsconventionally mounted to a bicycle and with the bicycle oriented andused in a standard fashion unless otherwise indicated.

FIGS. 1 and 1 a are an overview of the derailleur assembly. The basicstructure of the electromechanical rear derailleur or gear changer 20includes a base member 22, also referred to as a “b-knuckle,” which isattachable to a bicycle frame 19 in a conventional manner and an outerlink 24 and an inner link 26, which is pivotally attached to the basemember by link pins 28 a-d, for example. A moveable member or assembly30, also known as a “p-knuckle,” is pivotally connected to the outer andinner links at an end opposite the base member to permit displacement ofthe moveable assembly relative to the base member 22.

The outer link 24 and inner link 26 taken together may be consideredcomponents of a linkage or link mechanism 32, for example aparallelogram-type link mechanism. Cage assembly 34 is pivotallyconnected to moveable assembly 30 in a conventional manner. A bicyclechain 36 may be engaged with a sprocket of a conventional sprocketassembly 38 and positioned in the cage assembly 34 in a conventionalmanner and can be shifted from one sprocket to another of the sprocketassembly by the movement of moveable assembly 30 and cage assemblyrelative to base member 22 in a lateral direction when mounted.

The derailleur 20 is of the “Straight-P” or straight parallelogram typein contrast to a “slant parallelogram” type derailleur. Straight-Pderailleurs, or in other words non-slanted parallelogram derailleurs,have a linkage 32 with the pivot axes “PA” of the pins 28 (see FIG. 5b )forming the joints of the linkage substantially perpendicular (i.e.,within a few degrees) to the axial A′ direction, e.g., the mounting axis(see FIG. 2b ). The mounting axis may be defined by the axis of amounting bolt “B” of the derailleur or the axis of the hanger opening ofthe bicycle frame dropout, for example, (not shown). The pivot axes mayalso be considered parallel to the planes defined by the sprockets 38(FIG. 1). This causes the moveable assembly 30 to move substantiallyhorizontally. Also, the pivot axes PA may be vertical or non-vertical(see FIG. 1).

Because derailleur 20 is a straight-P, it has an offset jockey wheel 42,meaning that the rotational axis of the jockey wheel is not coincidentwith, i.e., is offset from, the axis of rotation of the cage about thep-knuckle 30, to accommodate the varying diameters of the sprockets 38.The derailleur may also be equipped with a damper assembly 40 and a cagelock 41 at the p-knuckle as is known in some mechanical derailleurs.

A gearbox 44 that is disposed in and/or forms part or all of theb-knuckle 22 drives the linkage 32 and the cage assembly 34 through therange of motion shown in FIGS. 2a and 2b . The gearbox 44 comprises atransmission 80.

Referring to FIG. 15a (which is section C-C of FIG. 1a ) the gearbox 44includes an output shaft 46. A drive arm 48 is mounted on the outputshaft 46 via a castellated geometry that engages with a correspondingcastellated geometry on the drive arm. The drive arm 48 and the outputshaft 46 are thereby rotatably fixed to one another.

In order to drive the linkage 32 in the inboard direction, i.e., towardthe larger diameter ones of the sprockets 38, the output shaft 46 andthe drive arm 48 is rotated by the gearbox 44 clockwise in FIG. 15a ,which drives the inner link 26 clockwise via a direct engagement betweenthe drive arm and a projection 50 on the inner link. In order to drivethe linkage 32 in the outboard direction, i.e., toward the smallerdiameter sprockets 38, the output shaft 46 and the drive arm 48 rotatecounterclockwise in FIG. 15a , which drives the inner link 26counterclockwise via engagement with a preloaded clutch spring 52, theposition and function of which will be described later. In other words,the drive arm 48 does not directly push on the inner link 26 to drive itin the outboard direction. Rather, the drive arm 48 pushes on the clutchspring 52, and the clutch spring drives the inner link 26 in theoutboard direction. The drive arm 48 and clutch spring 52 are considereda clutch 192, to move the derailleur or decouple the transmission fromthe derailleur as will be explained in more detail below.

As shown in FIG. 3 (which is section E-E of FIG. 2a ), a biasing spring54 is disposed around one of the linkage pivot pins 28 b. One leg 54 aof the biasing spring 54 engages the outer link 24, and the other leg(not shown) engages the base member 22. The biasing spring 54 may be anextension spring 54′ (FIG. 2a ). The action of the biasing spring 54urges the linkage 32 in the outboard direction to take the backlash outof the gearbox 44 and linkage.

FIG. 14 (which is section B-B of FIG. 1a ) shows the low limit screw 56.The low limit screw 56 is disposed in the gearbox assembly 44, and byadvancing and retracting the screw the inboard range of motion of theinner link 26 is limited. The limit screw 56 is adjusted in a tool-freemanner, by turning the limit screw 56 by hand. This tool-free designgreatly reduces the maximum torque that the limit screw 56 sees sincethe human hand can exert a at less torque on the screw than a human handaided by a screwdriver or other tool, and therefore greatly limits theforce exerted on the gears (see FIG. 7) of the gearbox 44 by the limitscrew. This is desirable because excessive force on the gears couldbreak them.

FIG. 7 is an exploded view of the gearbox assembly 44. The gearboxassembly 44 may form the structural part of the b-knuckle 22. As shownin FIG. 7, a motor module 60 (described in detail later) is received inan opening 62 in the bottom of the housing 64 of the gearbox 44 and issecured with fasteners 66, for example, six screws. The housing 64includes a pogo pin/seal assembly 68 (described in detail below))received in a recess 70 in the rear wall 72 of the gearbox housing 64and is secured with fasteners 74, for example, two screws.

An overview of the motor module 60 is shown in FIG. 8. A motor 76 isattached to a motor module base 78, which may be a plasticinjection-molded element or elements of any suitable material, and themajority of the transmission 80 is built up on axles 82 that arereceived in the base 78. A plate 104, which may be stamped metal or anysuitable material, is attached to the base 78, by screws for example,and supports the other end of the axles 82 of one or more of the gears,for example three of the gears.

The gearbox 44 includes a position detector 84 (see FIGS. 10, 11). Gearsassociated with the position detector, which will be described in moredetail hereinbelow, are located on or near the motor module base 78. PCboards 86 comprising circuitry for operating various functions of thederailleur 20 are connected together by flexible cables 88. The PCboards 86 may be three rigid boards or any suitable number of boards.Two of the three PC boards 86 may be screwed to the base 78, and theother PC board may be soldered to the back of the motor 76, for example.A flexible seal 90 is provided on the base 78 to seal between the baseand a motor module housing 92 after the base is assembled to the motormodule housing.

FIG. 9 is a section view of the motor module 60, showing a cross sectionof the motor 76 (section H-H of FIG. 8b ). Referring to FIG. 9, themotor 76 may be attached to the motor module base 78 with two screws(not visible in this view). A worm 94 is fixed to a shaft 96 of themotor 76, and a distal end 98 of the motor shaft is received in abearing 100, such as a ball bearing, which is, in turn, received in themotor module base 78. A worm wheel 102 is engaged with the worm 94.

FIG. 10 is a section view of the gearbox 44, showing three of the gearassemblies (section K-K of FIG. 7a ). Referring to FIG. 10, one end ofeach of the three axles 82 may each be rotatably received in the motormodule base 78, and the other end of each axe is received in acorresponding hole in the previously discussed metal plate 104. Threegear assemblies 106 a-c of the transmission 80 are rotatably received onthe three axles 82, respectively. The gear assembly 106 a on the rightin FIG. 10 has the worm wheel 102 on the bottom. The worm wheel 102, asdiscussed earlier, is engaged with the worm 94 on the motor shaft 96(see FIG. 7a ). The worm wheel 102 is rigidly attached to a first piniongear 108 that is coaxial therewith. The first pinion gear 108 is engagedwith a spur gear 110 that is rotatably received on the middle of thethree axles 82 b. This spur gear 110 is rigidly attached to a secondpinion gear 112 that is coaxial therewith. The second pinion gear 112 isengaged with a second spur gear 114 that is rotatably received on theaxle 82 c shown on the left in FIG. 10. The second spur gear 114 isrigidly attached to a third pinion gear 116 that is coaxial therewith.The third pinion gear 116 is engaged with an output gear 118 (see FIG.7a ) of the gearbox 44 (not visible in this section view). It shouldalso be noted that the axle 82 c shown on the left in FIG. 10 has itstop end supported in a bearing 120 in the motor module housing 92, whichadds a substantial amount of support to the metal plate 104. In otherwords, the metal plate 104 is supported by the leftmost axle 82 c, whichin turn is supported by the bearing 120 in the motor module housing 92.

FIG. 3 is a section view of the derailleur 20, showing a cross sectionof the two linkage pivot pins 28 a, b located by the b-knuckle 22(section EE of FIG. 2a ). Referring to the right hand side of FIG. 3,the output gear 118 of the gearbox 44 has a toothed portion 122 and twotubular portions 124 a, b projecting from either side of the toothedportion. The lower tubular portion 124 a is rotatably received in abearing in the motor module base 78, and the upper tubular portion 124 bis rotatably received in a bearing in the motor module housing 92. Theend of the lower tubular portion 124 a has the aforementionedcastellated geometry that engages the drive arm 48 as previouslydescribed (see FIG. 15a ). The inner link 26 has two arms 126 a, b, oneof which is located above the upper tubular portion 124 b of the outputgear 118, and the other of which is located below the lower tubularportion 124 a of the output gear. A hole 128 in the inner link arms 126a, b is coaxial with a hole 130 in the output gear 118, and theassociated link pin 28 a is received in these holes. The link pin 28 ais rotatable relative to the output gear 118, but is preferablyrotatably fixed to the inner link 26.

FIG. 11 is a section view of the gearbox 44, showing a cross section ofthe position detector 84. The position detector 84 is used to determinethe position of the derailleur by sensing rotation of the transmission80 (see FIG. 8). The position detector 84 includes a sensor in the formof a position detector chip 132, a position detector gear 134, aposition detector magnet 136, and an optional position detector gearbiasing gear 138 (section J-J of FIG. 7a ). Referring to FIG. 11, theposition detector gear 134 is rotatably mounted on a position detectoraxle 140, which is supported by the motor module base 78. The positiondetector gear 134 engages the output gear 118. A magnet holder 142 isfixed to the position detector gear 134, and the position detectormagnet 136 is fixed to the magnet holder. Thus, the position detectorgear 134, magnet holder 142, and magnet 136 all rotate together as aunit.

A position detector gear biasing gear axle 144 is supported by the motormodule base 78. The position detector gear biasing gear 138 is rotatablyreceived on the position detector gear biasing gear axle 144. One leg ofa torsion spring 146 is engaged with the motor module base 78, and theother leg of the torsion spring is engaged with the position detectorgear biasing gear 138. Thus, the torsion spring 146 exerts a torque onthe position detector gear biasing gear 138, which in turn exerts atorque on the position detector gear 134 to effectively eliminate anyplay or backlash between the position detector gear and the output gear118.

FIG. 12 is a section view of the motor module 60, showing a crosssection of the means by which the position detector chip 132 isaccurately located relative to the position detector magnet 136 (sectionG-G of FIG. 8a ). Referring to FIG. 12, a position detector chip 132 isdisposed on one of the three PC boards 86. A magnet guide 148 has twoprojections 150, which may be cylindrical, and which fit into twocorresponding holes 152 in the PC board 86. Two fasteners, e.g., screws,are inserted into the projections 150 to fasten the magnet guide 148 inplace on the PC board 86. Thus, the PC board 86, position detector chip132, magnet guide 148, and two screws form a subassembly. Duringassembly of the motor module 60, this subassembly is assembled to themotor module such that the magnet 136 is received in the magnet guide148. Thus, the axis of the position detector chip 132 is accuratelyaligned to the axis of the position detector magnet 136.

In order to prevent rotation of the PC board 86 relative to the motormodule 60, a slot 154 in the other end of the PC board engages a boss156 on the motor module base 78 (see FIG. 11). Again referring to FIG.11, a screw 158 is then screwed into a hole in the boss 156 until thescrew bottoms out on the boss. In this manner, the alignment between theposition detector chip 132 and the position detector magnet 136 is heldvery accurately. An optional compression spring 160 biases the PC boardassembly 86 downwards in FIG. 11. Alternatively, the magnet guide 148could have geometry that locates directly on the position detector chip132, rather than locating in two holes 152 in the PC board 86.

FIG. 13 is a section view of the gearbox 44, showing a cross section ofa button 162 and its actuator assembly 164 (section A-A of FIG. 1a ).The button 162 may be an electrical component on the PC board 86. Theactuator assembly 164 includes a plunger 166, return spring 168, O-ringseal 170, and retaining clip 172. When the plunger 166 is pressed by theuser, it actuates the button 162. Also visible towards the bottom ofFIG. 13 is an LED 174, which is another component on the PC board 86.This LED 174 shines through a clear lens 176 (also partially visible inFIG. 13) in the motor module base 78.

FIGS. 5a and 5b show the derailleur 20 with a power source 178, whichmay be a battery, installed (FIG. 5a ) and with the power source removed(FIG. 5b ). The cage assembly is omitted in these views for clarity. Thebattery may be a rechargeable battery and may be of the lithium-polymervariety.

FIGS. 6 a, b, c (section D-D of FIG. 2a ) show the electrical andmechanical connectivity between the battery 178 and the derailleur 20,and also show the procedure for removing the battery from thederailleur. Referring to FIGS. 6 a, b, c, and FIG. 7, the pogo pinassembly 68 includes a pogo pin base 180, a pogo pin base seal member182, and two pogo pins 184 (only one visible), two return springs 186(one visible), and two O-rings 188 (one visible). The pogo pin assembly68 may be attached to the motor module housing 92 with two screws asshown in FIG. 7. Referring to FIGS. 6 a, b, c, one end of the returnsprings 186 contacts the pogo pin 184, and the other end of the returnsprings contacts electrical contact pads 190 (FIG. 7) on a PC board 86.Thus, when the battery 178 is installed as shown in FIG. 6a ,electricity can flow from the battery, through the pogo pin 184, throughthe return spring 186, and into the PC board 86. The power supply 178may be mechanically retained on the derailleur 20 with a catch 196.

Turning to FIGS. 15a-c , and also FIG. 4, the derailleur 20 is equippedwith a breakaway mechanism or clutch 192 that protects the gears 106 ofthe transmission 80 in the gearbox 44 (FIG. 8) in the event of a crashor other side impact to the derailleur. FIGS. 15a, b and c , show asection view of the derailleur 20 (section C-C of FIG. 1a ) with theclutch 192 in its non-actuated (i.e. normal) position (FIG. 15a ), itspartially actuated position (FIG. 15b ), and its fully actuated position(FIG. 15c ). During normal riding, the elements of the clutch 192 arearranged as shown in FIG. 15a , comprising the spring 52 and drive arm48.

In the event of a crash or other side impact (a force directed from leftto right in FIGS. 15a, b and c ), if the force of the impact overcomesthe preload in the torsion-type clutch spring 52, the links of thelinkage 32 rotate clockwise about their pivot pins 28, deflecting theleg 52 a of the spring as shown in FIG. 15b . Thus, the linkage 32 isable to move without imparting any movement to the gears 106 in thegearbox 44. When the impact force is removed from the derailleur 20, thespring leg 52 a will push against the drive arm 48 and cause thederailleur to go back to its normal state shown in FIG. 15 a.

In the event of a more forceful crash or side impact, the links oflinkage 32 can rotate clockwise about their pivot pins 28 all the way tothe position shown in FIG. 15c . In this position, further clockwiserotation of the links 32 is prevented when the drive arm 48 andprojection 50 interact and any additional force imparted to the linkswill be transferred to the gears 106.

Another aspect of the invention that protects the gears 106 is thestraight-P arrangement of the derailleur 20. When a bicycle is movingover rough terrain, the p-knuckle 30 of the derailleur 20 experiencesforces in the vertical direction. In a slant P derailleur, the axes ofthe link pins are angled relative to the vertical direction, and theseforces can be transmitted through the linkage/parallelogram, impartingundesired forces to the gears in the transmission, since the linkage isable to move in a direction that has a substantial vertical component.The motion of the linkage 32 of the present invention, however, issubstantially lateral, rather than vertical, at least because of thevertical orientation of the link pins 28, and therefore the elements ofthe derailleur are relatively isolated from the vertical forces createdwhen the bicycle is moving over rough terrain, thereby protecting thegears 106 of the transmission 80 from damage. Preferably, the axes ofthe link pins 28 are all within 30 degrees of vertical (in addition tobeing normal to the axial A′ direction).

A radio chip 194 is positioned on the PC board 86 in such a way tomaximize radio signals transmitted between the derailleur 20 and ashifter (or other control devices). Referring to FIG. 11, the radio chip194 is positioned on the lower portion of the rightmost PC board 86 suchthat it is substantially housed in the motor module base 78, which maybe made of plastic, or any suitable material that does not interferewith the transmission of radio signals. In other words, the radio chip194 is preferably not positioned on the upper portion of the PC board86, because the upper portion of the PC board is substantially housed inthe motor module housing 92, which is preferably made of aluminum, whichis a material that is not conducive to transmitting radio signals.

While this invention has been described by reference to a particularembodiment, it should be understood that numerous changes could be madewithin the spirit and scope of the inventive concepts described.Accordingly, it is intended that the invention not be limited to thedisclosed embodiment, but that it have the full scope permitted by thelanguage of the following claims.

The invention claimed is:
 1. An electromechanical rear derailleur for a bicycle, comprising: a base member attachable to the bicycle along a mounting axis; a movable member having a cage assembly attached thereto; a linkage including pivot axes oriented substantially perpendicular to the mounting axis, the linkage coupling the movable member to the base member and operative to enable movement of the movable member relative to the base member; a power source disposed on the rear derailleur rearward of the pivot axes; a motor electrically connected to the power source; and a transmission coupled to and actuated by the motor to move the movable member.
 2. The rear derailleur of claim 1, wherein the power source is disposed on or in the base member.
 3. The rear derailleur of claim 1, wherein the linkage includes an outer link member and an inner link member.
 4. The rear derailleur of claim 1, wherein the linkage includes link pins on which the linkage pivots, the link pins defining the pivot axes.
 5. The rear derailleur of claim 4, wherein the transmission includes a plurality of gears rotatable about a plurality of gear axes, respectively, wherein the gear axes are substantially parallel to the pivot axes.
 6. The rear derailleur of claim 5, wherein the transmission is disposed on or in the base member.
 7. The rear derailleur of claim 6, wherein the motor is disposed on or in the base member.
 8. The rear derailleur of claim 7, wherein the power source is disposed on or in the base member.
 9. The rear derailleur of claim 7, wherein the linkage includes an outer link member and an inner link member.
 10. The rear derailleur of claim 4, further comprising a clutch between the movable member and the transmission, the clutch moving the movable member responsive to operation of the transmission.
 11. The rear derailleur of claim 10, the clutch including a drive arm coupled to the transmission and a clutch spring in contact with the drive arm.
 12. The rear derailleur of claim 11, wherein the transmission includes an output gear and the drive arm is coupled to the output gear.
 13. The rear derailleur of claim 12, wherein the clutch spring is disposed on an inner link member of the linkage.
 14. The rear derailleur of claim 12, wherein the clutch spring is disposed about the link pin that attaches an inner link member of the linkage to the movable member.
 15. The rear derailleur of claim 4, wherein the motor has a motor shaft with a motor shaft axis that is perpendicular to the pivot axes.
 16. The rear derailleur of claim 1, wherein the linkage includes link pins on which the linkage pivots, the link pins defining the pivot axes and the transmission includes a plurality of gears rotatable about a plurality of gear axles, respectively, wherein at least some of the gear axles have gear axle axes that are substantially parallel to the pivot axes.
 17. The rear derailleur of claim 1, wherein the pivot axes are non-vertical.
 18. An electromechanical rear derailleur for a bicycle, comprising: a base member attachable to the bicycle; a movable member having a cage assembly attached thereto; a linkage coupling the movable member to the base member and operative to enable movement of the movable member relative to the base member; a power source; a motor electrically connected to the power source; a transmission coupled to and actuated by operation of the motor to move the movable member; a position detector, comprising: a magnet; a sensor to sense relative rotation between the magnet and the sensor; a magnet guide sized and shaped to guidingly receive a portion of the magnet and position the sensor and magnet within an effective range of each other; and a magnet holder disposed in the rear derailleur and coupled to the transmission, the magnet held by the magnet holder; and a PC board positioned in the base member and wherein the sensor is disposed on the PC board in position to sense motion of the magnet.
 19. The rear derailleur of claim 18, wherein the magnet is rotated by the transmission.
 20. The rear derailleur of claim 18, wherein the magnet guide is disposed on the PC board and the magnet extends from the magnet holder.
 21. The rear derailleur of claim 20, wherein the magnet holder is attached to a position detector gear.
 22. The rear derailleur of claim 21, wherein the position detector gear is contact with and actuated by an output gear of the transmission.
 23. The rear derailleur of claim 22, further comprising a position detector gear biasing gear disposed in the derailleur and coupled to the position detector gear to reduce backlash thereof.
 24. The rear derailleur of claim 1, wherein the cage assembly comprises at least one wheel configured to engage with a chain.
 25. The rear derailleur of claim 1, wherein the power source is a battery configured for removable attachment to the base member. 